Methods and apparatus for polishing and planarization

ABSTRACT

A pad for processing substrates such as a pad for CMP and methods of using the pad: the pad is capable of allowing the substrate to be optically monitored during the process. In one embodiment, at least a portion of the pad includes an optical filter for attenuating optical noise so that optical signals used for monitoring the substrate provide a more accurate representation of the process status. The optical filter is capable of transmitting the optical signal while reducing the amount of optical noise. In another embodiment, the surface of the filter is recessed from the polishing surface of the pad so that the filter surface is subjected to less abrasion during polishing processes and during pad conditioning.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. Provisional PatentApplication, Serial No. 60/278498, filed on Mar. 23, 2001, and U.S.Provisional Patent Application No. 60/285634, filed on Apr. 20, 2001;the entire contents of all of these applications are incorporated hereinby this reference.

TECHNICAL FIELD

[0002] This invention relates to pads and methods of using and makingthe pads for applications such as chemical mechanical planarization(CMP) and polishing of substrates such as semiconductor substrates,wafers, metallurgical samples, memory disk surfaces, optical components,lenses, electronic devices, and wafer masks. More particularly, thepresent invention relates to CMP pads and pads for polishing that arecapable of filtering optical signals used for process monitoring.

BACKGROUND

[0003] The removal of material from the surface of a substrate so as topolish or planarize the substrate is essential in numerous technologies.For example, electronic devices typically include a substrate, such as asilicon or group III-IV types of wafers, on which numerous integratedcircuits have been formed. Integrated circuits are integrated into asubstrate by patterning regions in the substrate and layers on thesubstrate. To achieve high yields, it is crucial to start with asubstantially flat substrate; consequently, it is often necessary toplanarize the substrate surface. If the process steps of devicefabrication are performed on a substrate surface that is not planar,various problems can occur which may result in a large number ofinoperable devices. For example, in fabricating modem semiconductorintegrated circuits, it is necessary to form conductive lines or similarstructures above a previously formed structure. However, prior surfaceformation often leaves the top surface topography of a wafer highlyirregular, with bumps, areas of unequal elevation, troughs, trenches,and other similar types of surface irregularities. Global planarizationof such surfaces is necessary to ensure adequate depth of focus duringphotolithography, as well as removing any irregularities and surfaceimperfections during the sequential stages of the fabrication process.

[0004] Although several techniques exist for achieving substrate surfaceplanarity, processes employing chemical mechanical planarization orpolishing techniques have been widely used to planarize the surface ofwafers during the various stages of device fabrication in order toimprove yield, performance and reliability. In general, chemicalmechanical polishing (CMP) involves moving a wafer under a controlledpressure with pre-defined velocity over the surface of a polishing pad,while the aforementioned surface is covered or saturated with polishingslurry. Some processes involve moving a pad over a stationary substrate.

[0005] An important part of processes such as CMP is the determinationof process endpoint. In addition, it is often desirable to be able tomonitor the surface of the substrate throughout the process. There arestandard technologies for in-situ monitoring and endpoint determinationfor CMP. Typically, the standard technologies are based on laserinterferometer, phase-shift optical thickness measurement, reflectancechange measurements, and similar techniques. The standard techniques,typically, require a transparent window in the CMP pad so that emittedlight from a signal source can reach the substrate surface and thereflected light or signal can reach a detector.

[0006] Although the standard processes and apparatus for monitoring andendpoint detection for process like CMP are in common use, the standardtechnology still has problems. The obstacles encountered for copper CMPprocesses exemplify some of the problems with standard CMP monitoringtechnologies. Specifically, copper CMP requirements present essentiallyall process problems typically for CMP plus some unique aspects thatwill also arise in other advanced CMP situations. One of the uniqueaspects of copper CMP is formation of water-soluble copper salts, coppercompounds, and copper-rich precipitates. The salts, compounds, andprecipitates result in polishing by-products having blue-green colors.In addition, copper CMP by-products have a maximum transmission ofvisible light in the same region. Consequently, the copper by-productscan significantly interfere with the optical signals used as part ofstandard CMP monitoring and end pointing. In other words, the presenceof the copper by-products can introduce additional optical noise for theoptical signal detector used for monitoring the CMP process.

[0007] Furthermore, the standard technologies for determining CMPendpoints are usually directed toward very advanced methods oftransmitting optical signals to the polishing surface and receivingreflected optical signals from the surface being polished. However, thestandard methods and apparatus fail to recognize the fact that thematerial for conveying the optical signal plays a crucial role in thequality of the signal. The standard methods and apparatus for monitoringCMP processes have neglected to improve the optical transmissioncharacteristics of the materials used in optical process monitoring.

[0008] The standard technology also has other problems. In the standardtechnology, it is preferable to have the window flushed or substantiallyflushed with the polishing pad surface. Examples of the standardtechnology can be found in U.S. Pat. No. 5,605,760, U.S. Pat. No.6,171,181, and U.S. Pat. No. 6,0454,39. A problem with the standardtechnology is that during the polishing process, abrasive particles inthe polishing slurry abrade the surface of the window material used forprocess monitoring and end-point-detection.

[0009] Another problem is that, during pad conditioning, diamondparticles in the conditioning disk abrade the surface of the window forprocess monitoring and end-point-detection. The surface roughness of thewindow increases with operation time. In other words, the transmittanceof the window decreases with increasing operation time. Theendpoint-detection system fails when the transmittance of the windowbecomes very low. The transmittance value caused end-point-detectionfailure may also depend on the polishing equipment. Specifically, thelifetime of window material can determine the lifetime of the polishingpad.

[0010] Although pads for processes such as polishing and planarizationare in extensive use, a need remains for improved pads which provideeffective planarization across substrates such as electronic devices andthat are capable of allowing improved process monitoring. Specifically,pads are needed that are suitable for using optical signals that arehigher in absolute value and more accurate for monitoring CMP processes.Improved CMP processes are needed so that optically monitoring the CMPprocess can be done with less signal loss and with reduced opticalnoise. Furthermore, there is a need for pads that have high durabilityin addition to allowing in situ process monitoring for CMP processes.Pads are needed that can be used for longer periods of time before thepad must be replaced. Improved processes are needed so that processessuch as CMP processes can be effectively performed for longer periods oftime before signal transmission properties of the window material becomeunsatisfactorily low. There is a need for pads that have high durabilityin addition to allowing in situ process monitoring for polishingprocesses.

SUMMARY

[0011] This invention pertains to improved methods and apparatus formonitoring and processing substrates such as for polishing processes andfor CMP processes. Embodiments of the present invention are particularlysuited for continuous film thickness monitoring as well as endpointdetection of CMP processes. The present invention seeks to overcome oneor more of the deficiencies of the standard technologies for opticallymonitoring and processing surfaces.

[0012] An aspect of the present invention is a pad for processingsubstrates such as, for example, CMP of substrates. The pad is capableof allowing the substrate to be optically monitored during the CMPprocess. At least a portion of the pad includes an optical filter forattenuating optical noise so that optical signals used for monitoringthe substrate provide a more accurate representation of the CMP processstatus. The optical filter is capable of transmitting the optical signalwhile substantially reducing the amount of optical noise.

[0013] In one embodiment of the present invention, the pad includes anoptical filter for transmitting the optical signal used in monitoringthe CMP process. In addition to transmitting the optical signal, theoptical filter removes optical noise. In a further embodiment, theoptical filter includes fibers for increasing the strength of theoptical filter.

[0014] In another embodiment of the present invention, the opticalfilter uses an antireflection coating to improve the efficiency oftransmitting the optical signals through the filter. Optionally, theanti-reflective coating may be put on the bottom of the optical filter(the side furthest from the substrate), top of the optical filter (theside closest to the substrate), or any location that reduces reflectionloss.

[0015] Another aspect of the present invention is a method formonitoring CMP processes. In one embodiment, the method is carried outwith a CMP pad capable of filtering predetermined frequencies of lightso as to remove optical noise. The method includes the step of polishinga substrate surface with the pad using chemical mechanical polishing.The method also includes the step of directing an original opticalsignal toward the substrate surface and generating a reflected opticalsignal from the substrate surface. The method further includes the stepof using the pad to filter optical noise from at least one of theoriginal optical signal and the reflected optical signal. After the stepof filtering the optical noise is the step of measuring the reflectedoptical signal to determine the status of the CMP process.

[0016] Another aspect of the present invention is a pad for processingsubstrates such as for example CMP of substrates. The pad is capable ofallowing the substrate to be optically monitored during the CMP processfor longer periods of time. The pad includes a window material. Thesurface of the window material has a recess relative to the polishingsurface of the polishing pad instead of being flushed with the surface.

[0017] One embodiment of the present invention is a CMP pad foroptically monitoring CMP processes, the pad having a polishing surface;at least a portion of the pad comprising a light transmissible material,i.e., window material. The window material is capable of transmitting anoptical signal for optically monitoring CMP processes; the windowmaterial has a surface that is recessed relative to the polishingsurface of the pad. The amount of the recess is sufficient to reduce theabrasion of the window material during polishing and during padconditioning.

[0018] Yet, another aspect of the present invention includes electronicdevices and other products made using the methods and apparatus of thepresent invention.

[0019] It is to be understood that the invention is not limited in itsapplication to the details of construction and to the arrangements ofthe components set forth in the following description or illustrated inthe drawings. The invention is capable of other embodiments and of beingpracticed and carried out in various ways. In addition, it is to beunderstood that the phraseology and terminology employed herein are forthe purpose of description and should not be regarded as limiting.

[0020] As such, those skilled in the art will appreciate that theconception, upon which this disclosure is based, may readily be utilizedas a basis for the designing of other structures, methods and systemsfor carrying out aspects of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

[0021] Further, the purpose of the foregoing abstract is to enable theU.S. Patent and Trademark Office and the public generally, andespecially the scientists, engineers and practitioners in the art whoare not familiar with patent or legal terms or phraseology, to determinequickly from a cursory inspection the nature and essence of thetechnical disclosure of the application. The abstract is not intended todefine the invention of the application, which is measured by theclaims, nor is the abstract intended to be limiting as to the scope ofthe invention in any way.

[0022] The above and still further features and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed descriptions of specific embodiments thereof,especially when taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a cross section diagram of an embodiment of the presentinvention.

[0024]FIG. 2 is a graph of optical transmission characteristics for anoptical filter according to an embodiment of the present invention.

[0025]FIG. 3 is a cross section diagram of an embodiment of the presentinvention.

[0026]FIG. 4 is a cross section diagram of an embodiment of the presentinvention.

[0027]FIG. 5 is a cross section diagram of an embodiment of the presentinvention.

[0028]FIG. 6 is a cross section diagram of an embodiment of the presentinvention.

DESCRIPTION

[0029] The operation of embodiments of the present invention will bediscussed below, primarily, in the context of planarizing and/orpolishing substrates such as substrates used for fabrication ofelectronic devices. However, it is to be understood that embodiments inaccordance with the present invention may be used for applications suchas planarizing and/or polishing substrates such as metallurgicalsamples, memory disk surfaces, optical components, lenses, electronicdevices, and wafer masks. Further, it us to be understood thatembodiments in accordance with the present invention may be used forapplications such as offline and non-in-situ optical metrologyapplications where optical losses are critical factors in systemperformance.

[0030] In the following description of the figures, identical referencenumerals have been used when designating substantially identicalelements or steps that are common to the figures.

[0031] One embodiment of the present invention is a pad for CMP. The padis capable of substantially transmitting an optical signal formonitoring a CMP process. The pad is also capable of optical filteringso that optical noise is substantially prevented from causinginaccuracies in the optical signal measurements used for monitoring theCMP process.

[0032] Reference is now made to FIG. 1 wherein there is shown across-section diagram of a portion of a CMP pad 15 according to oneembodiment of the present invention. Pad 15 includes a polymer sheet 20and an optical filter 25. Polymer sheet 20 has chemical and physicalproperties for performing chemical mechanical polishing. Polymer sheet20 has a hole 22 extending from a first side of sheet 20 through to theopposite side of sheet 20.

[0033] Optical filter 25 is capable of transmitting optical signals formonitoring the CMP process. Optical filter 25 is also capable ofattenuating selective wavelengths of light corresponding to thewavelengths of optical noise. Preferably, optical filter 25 issubstantially impermeable to fluid transfer.

[0034] Polymer sheet 20 and optical filter 25 are connected so thatoptical filter 25 substantially prevents fluid communication throughhole 22 from the first side of polymer sheet 20 to the second side ofpolymer sheet 20. Optical filter 25 allows transmission of an originaloptical signal for monitoring the CMP process so that the optical signalcan impinge upon the surface of a substrate during CMP. Optical filter25 also allows transmission of a reflected optical signal from thesurface of the substrate during CMP.

[0035] Polymer sheet 20 can be made using a variety of techniques suchas those typically used for making CMP polishing pads. Methods of makingstandard CMP polishing pads are well known in the technical and patentliterature. For more information about polishing pads, see WIPOPublication W096/15887, the specification of which is incorporatedherein by reference. Other representative examples of polishing pads aredescribed in U.S. Pat. Nos. 4,728,552, 4,841,680, 4,927,432, 4,954,141,5,020,283, 5,197,999, 5,212,910, 5,297,364, 5,394,655 and 5,489,233, thespecifications of which are also each incorporated herein in theirentirety by reference.

[0036] In one configuration, polymer sheet 20 comprises a moldedcomposite plastic that includes an embedded matrix, such as polyesterfibers. The matrix is impregnated with a polymer resin such aspolyurethane. In another embodiment, the polymer sheet includes anon-woven felt and a polymer resin; the felt is impregnated with theresin to form the polymer sheet.

[0037] In one embodiment of the present invention, optical filter 25 ismade of a cast plastic such as polyurethane. In a preferred embodiment,optical filter 25 is made from cast polyether urethane. In a furtherembodiment, the thickness of the filter is held in the range of about0.040 to about 0.042 inch (1.0 mm to about 1.1 mm).

[0038] Generally, preferred embodiments of the present invention usematerials that are capable of withstanding substantially all chemicaland physical rigors associated with CMP process. Some of the typicalconditions that the materials may need to withstand are pH range from 2to 14 and abrasion resistance <0.0005 inch (12 micrometers) thicknessloss after 1000 wafer buffs.

[0039] Optical filter 25 may operate according to a variety ofwell-known techniques for optical filtering. For instance, opticalfilter 25 may operate on the principle of selectively absorbingpredetermined wavelengths of light, or optical filter 25 may operate onthe principle of selectively enhancing optical transmission ofpredetermined wavelengths. Alternatively, optical filter 25 may operateon the principle of selectively reflecting predetermined wavelengths oflight. In addition, a combination of optical filtering techniques maybeused in some embodiments of the present invention.

[0040] In one embodiment of the present invention, the optical filteringcharacteristics for filter 25 are created by adding a dye to a plasticbody included in optical filter 25. The addition of the dye causes theplastic to transmit a band of wavelengths that includes the wavelengthsfor the original optical signal and the reflected optical signal usedfor monitoring the CMP process. Examples of suitable dyes that can beused are diazo type colorants such as those available from GAFCorporation, phthalocyanine type green and blue colorants such as thosemade by E.I.DuPont, Inc. In some embodiments of the present invention,the amount of dye ranges from about 1% to about 5% by volume and haveoptical transmission greater than about 85% in a specified wavelengthregion.

[0041]FIG. 2 shows the optical transmission characteristics of oneembodiment of the present invention. This embodiment includes a castplastic with a dye added to enhance the optical transmission propertiesof an optical filter in the range of about 600 nanometers. Specifically,addition of the dye causes the plastic to behave as a bandpass opticalfilter. It is to be understood that factors such as the opticalproperties of the CMP by-products and the choice of light source and/ordetector combination influence the selection of the dyes for embodimentsof the present invention. It is well understood that different dyes canbe added to cast plastic or other materials so as to cause opticaltransmission blocking or optical transmission enhancement foressentially any predetermined optical wavelength from the UV band downto the far infra-red end of the visible spectra.

[0042] In a further embodiment, optical filter 25 may also includemicrofibers 30 (shown FIG. 1) made of materials such as nylon, kevlar,kapton, and capron. The core density, individual diameters of filaments,filament spacing, and other properties are selected in such a way thatthe optical quality of filter 25 shows substantially no noticeabledegradation while maintaining mechanical properties having the followingvalues: Tensile strength >8000 pounds per square inch, Elongation atbreak <400%, Tear resistance >700 pounds per inch. Furthermore, theincreased strength of the filter material yields increased resistance toabrasion and increased resistance to cyclical stresses associated withCMP processes.

[0043] Preferably, microfibers 30 are suspended in the cast plastic soas to form a composite material having greater strength than that of thecast plastic without the reinforcing microfibers. Other well knowntechniques can be used to increase the strength of the plastic. Forexample, the strength can also be increased by methods such as addingmicrospheres and analogous methods.

[0044] The durability of the filter can also be increased by increasingthe hardness of the filter. The hardness of some of the plasticssuitable for embodiments of the present invention can be increased byadding hardeners to the plastic. For instance, hardeners such as1,4-butanediol, 2,3-butanediol, ethylene diamine, and trimethylolpropane can be added to the polyurethane to produce a final materialhardness in the range of 60 to 60D on the Shore D scale. The higherhardness of the filter reduces susceptibility of the filter toscratching by the slurry and/or scratching during processes such as padconditioning.

[0045] Reference is now made to FIG. 3 wherein there is shown a crosssection diagram of a portion of a CMP pad 15 according to the presentinvention. CMP pad 15 shown in FIG. 3 is substantially the same as thatdescribed for the CMP pad presented in FIG. 1. The CMP pad shown in FIG.3 also includes an antireflection coating 35. Anti-reflection coating 35is applied to optical filter 25 to reduce losses of optical signalintensity at the surface of optical filter 25 caused by changes in therefractive index. Without antireflection coatings, the signal loss dueto refractive index changes can equal about 4 percent of the signalintensity. However, use of the anti-reflection coating reduces the 4percent loss due to reflection. Embodiments of the present inventioninclude anti-reflection capabilities so that that reflection losses ofthe optical signal is less than 4%. Because of the selection of theantireflection properties, some embodiments of pads according to thepresent invention can have reflection losses in the range of about 0% toabout 3.8% and all subranges subsumed therein. Preferably, thereflection losses are less than about 3.5%, and more preferably lessthan about 3% for the optical signal used for monitoring the process.

[0046] Optical filters according to some embodiments of the presentinvention are strong and mechanically stable. These characteristicsallow the optical filters to be used in embodiments of the presentinvention in a variety of shapes and sizes. Particularly advantageous isthat the smallest size is limited only by the choice of optical sourceand detector combination.

[0047] The mechanical strength of the filter and high light-transmissioncharacteristics allows a user to reduce the physical size of the filter,thus, reducing the “parasitic zone” within polishing region of thesubstrate. Furthermore, the superior optical signal transmissioncapabilities of the filter can enable the use of a reduced power lightsource for the optical signal. The lower power light source can, in somecases, reduce the parasitic photochemical effects that can occur withinthe polishing zone.

[0048] Reference is now made to FIG. 4 wherein there is shown a crosssection view of an embodiment of the present invention. Afrequency-tuned optical filter 25 is physically incorporated in apolishing pad 17. The location of the filter is essentially a matter ofdesigner choice and only depends on choice of optical signal source anddetector combination (the optical signal source and detector are notshown in FIG. 4). In order to minimize physical interactions between thesurface of filter 25 and the semiconductor wafer that is being polished,filter 25 is recessed about 0.001 inch (0.025 mm) to about 0.002 inch(0.050 mm) in reference to polymer sheet 20. In other embodiments,filter 25 could be flush with the surface of sheet 20 or recessedfurther depending on desired results. An example of a suitable polymersheet is a TWI 813 pad, commercially available from Thomas West, Inc.Use of a pad and sub-pad combination allows easy installation of filter25, particularly where there is a 1 mm to 1.5 mm ledge remaining on asub-pad 40 such as the TWI 817 sub-pad, commercially available fromThomas West, Inc. An adhesive 38 such as PSA-C and the sub-pad 40 arecapable of providing full circumferential support of the optical filter25.

[0049] An adhesive 42, such as PSA-C or equivalent from companies suchas Avery Dennison Company of Plainsville, Ohio, provides a substantiallyleak-tight seal between the CMP slurry media and electro-opticalcomponents located below the polishing pad environment. (Slurry mediaand electro-optical components are not shown in FIG. 4.) Sub-pad 40 isan optional feature; essentially the same type of installation can beaccomplished with substantially any type of pad that includes a backingadhesion layer.

[0050] In other embodiments, the pad includes a window material. As anoption, the window material may not have optical filtering capabilitiessuch as those described for the embodiments in FIGS. 1-3. The surface ofthe window material is positioned to be recessed relative to thepolishing surface of the polishing pad instead of being flushed with thesurface like the standard technology. By creating the recess, padmaintenance processes such as pad conditioning cause less damage to thewindow material. Specifically, the conditioning disk will have less orno contact with the window material and cause less scratching of thewindow material. In addition, there will be less abrasion of the windowmaterial during polishing processes. Consequently, the transmittance ofthe window material can be retained for longer operation times. To avoidexcessive accumulation of slurry particles, it is preferable for therecess to not be too large. A suitable recess range is about equal to orsmaller than about three fourths of the thickness of the pad. Apreferred recess range should be about equal to or smaller than abouthalf of the thickness of the pad.

[0051] Reference is now made to FIG. 5 wherein there is shown across-section view of a section of a polishing pad 15 according to oneembodiment of the present invention. Pad 15 includes a polymer sheet 20and a window material 26. Polymer sheet 20 has chemical and physicalproperties for performing chemical mechanical polishing. Polymer sheet20 has a hole 22 extending from a first side of sheet 20 through to theopposite side of sheet 20. Window material 26 is capable of transmittingoptical signals for monitoring the CMP process. In preferredembodiments, window material 26 is substantially impermeable to fluidtransfer.

[0052] Polymer sheet 20 and window material 26 are connected so thatwindow material 26 substantially prevents fluid communication throughhole 22 from the first side of polymer sheet 20 to the second side ofpolymer sheet 20. Window material 26 allows transmission of an originaloptical signal for monitoring the CMP process so that the optical signalcan impinge upon the surface of a substrate during CMP. Window material26 also allows transmission of a reflected optical signal from thesurface of the substrate during CMP. The surface of window material 26is positioned to be recessed relative to the polishing surface ofpolishing pad 15 instead of being flushed with the surface like thestandard technology. The window material is recessed so as tosubstantially minimize contact between the window material and aconditioning disk during pad conditioning processes. Therefore, thetransmittance of the window material can be retained for longeroperation times. To avoid excessive accumulation of slurry particles, itis preferable for the recess to not be too large. The preferred recessrange should be equal to or smaller than about half of the thickness ofthe pad. For some embodiments of the present invention, the amount ofthe recess is in the range of about 5% to about 75% of the thickness ofthe polishing pad or top pad in a stacked pad configuration. Thepreferred amount of the recess is in the range of about 5% to about 50%of the thickness of the polishing pad or the top pad in a stacked padconfiguration.

[0053] Reference is now made to FIG. 6 wherein there is shown across-section view of a section of a polishing pad. Window material 26is an integral part of polishing pad 17. The location of the windowmaterial is essentially independent and only depends on choice ofoptical signal source and detector combination (the optical signalsource and detector are not shown in FIG. 6). In order to minimizephysical interactions between the surface of window material 26 and thesemiconductor wafer that is being polished, window material 26 isrecessed about 5% to about 75% of the thickness of polymer sheet 20 inreference to polymer sheet 20. An example of a suitable polymer sheet isa TWI 813 pad, commercially available from Thomas West, Inc. Use of apad and sub-pad combination allows easy installation of the windowmaterial 26, particularly where there is a 1 mm to 1.5 mm ledge left ona sub-pad 40 such as the TWI 817 sub-pad, commercially available fromThomas West, Inc. An adhesive 38 such as PSA-C and the sub-pad 40 arecapable of providing full circumferential support of the window material26. An adhesive 42 such as PSA-C or equivalent by Avery Dennison Companyof Plainsville, Ohio provides a substantially leak-tight seal betweenthe slurry media and electro-optical components located below thepolishing pad environment (slurry and electro-optical components notshown in FIG. 6). Sub-pad 40 is an optional feature; essentially thesame type of installation can be accomplished with substantially anytype of pad that includes a backing adhesion layer.

[0054] Experiments have been done comparing the performance of CMP padsaccording to embodiments of the present invention and CMP pads of thestandard technology. Under analogous operating conditions, the CMP padsaccording to the standard technology can be operated for about 5-6 hoursbefore they need to be replaced. However, CMP pads, according toembodiments of the present invention where the window is recessed about300 micrometers, can be operated for about 9 hours or longer before thepads need to be replaced.

[0055] Clearly, there is a significant improvement in the operatinglifetime of pads according to embodiments of the present inventioncompared to pads of the standard technology. The longer operatinglifetimes of pads according to embodiments of the present invention,consequently, are expected to provide a lower cost of ownership forpolishing processes such as CMP processes. Furthermore, substrates,electronic devices, and other products produced using embodiments of thepresent invention are expected to have lower production costs as aresult of the present invention. Still further, production facilitiesusing embodiments of the present invention are expected to have higheroverall production efficiencies as a result of the longer operatingtimes for CMP processes using embodiments of the present invention.

[0056] While there have been described and illustrated specificembodiments of the invention, it will be clear that variations in thedetails of the embodiments specifically illustrated and described may bemade without departing from the true spirit and scope of the inventionas defined in the appended claims and their legal equivalents.

What is claimed is:
 1. A pad for optically monitoring and processing thesurface of a substrate, at least a portion of the pad comprising anoptical filter for attenuating optical noise; the optical filter beingcapable of transmitting an optical signal for optically monitoring thesubstrate.
 2. The pad of claim 1 wherein the optical filter is capableof enhanced optical transmission for frequencies near the frequencies ofthe optical signal.
 3. The pad of claim 1 wherein the optical filtercomprises a bandpass filter having a frequency transmission band so thatthe optical signal is substantially transmitted by the filter.
 4. Thepad of claim 3 wherein the bandpass filter has peak transmission in thewavelength range of about 450 nanometers to about 700 nanometers.
 5. Thepad of claim 4 wherein the bandpass filter has peak transmission at awavelength of about 580 nanometers.
 6. The pad of claim 1 wherein theoptical filter comprises a dye suspended in an optically transmissivematerial, wherein the dye alters the optical transmission properties ofthe optically transmissive material.
 7. The pad of claim 6 wherein theoptically transmissive material comprises a cast plastic.
 8. The pad ofclaim 6 wherein the optically transmissive material comprises apolyurethane.
 9. The pad of claim 8 wherein the dye is present atconcentrations of 1% to 5% by volume and provides optical transmissiongreater than about 85% in a specified region.
 10. A CMP pad foroptically monitoring CMP processes using an optical signal, the padcomprising: a) a polymer sheet having a first side and a substantiallyparallel second side, the polymer sheet having a hole extending from thefirst side to the second side; b) an optical filter, the optical filterbeing substantially impermeable to fluid transport, the optical filterbeing connected with the polymer sheet to substantially prevent fluidcommunication through the hole from the first side to the second side,the optical filter being capable of attenuating optical noise so thatmeasurements of the optical signal have reduced interference fromoptical noise.
 11. The CMP pad of claim 10 wherein the optical filtercomprises: a matrix of reinforcing fibers; and a cast plastic body, thefibers being integrated with the body so as to strengthen the body. 12.The CMP pad of claim 10 wherein the optical filter comprises: a dye; anda cast plastic body, the dye being suspended in the body, the dye havingoptical properties so that the presence of the dye in the body allowstransmission of a band of optical wavelengths while attenuatingtransmission of optical noise.
 13. The CMP pad of claim 10 wherein theoptical filter comprises polyurethane.
 14. The CMP pad of claim 10wherein the polymer sheet comprises polyurethane.
 15. The CMP pad ofclaim 12 wherein the dye concentration is from about 1% to about 5% byvolume and has optical transmission greater than about 85% in apredetermined wavelength region.
 16. The CMP pad of claim 10 wherein theoptical filter comprises an antireflection coating for increasing theefficiency of transmitting the signal.
 17. The CMP pad of claim 10wherein the polymer sheet comprises a polishing surface and the filteris recessed below the polishing surface a distance of about 5% to about75% of the thickness of the polymer sheet.
 18. A method of processmonitoring, the method being carried out with a pad capable of filteringpredetermined frequencies of light, the method comprising the steps of:i. removing material from a substrate surface with the pad; ii.directing an original optical signal at the substrate surface andgenerating a reflected optical signal from the substrate surface; iii.filtering optical noise from at least one of the original optical signaland the reflected optical signal using the pad; iv. measuring thereflected optical signal to determine the status of the process.
 19. Themethod of claim 18 wherein the step of filtering optical noise comprisesat least one step of reducing the intensity of optical noise ofwavelengths longer than about the wavelength of the original opticalsignal, reducing the intensity of optical noise of wavelengths shorterthan about the wavelength of the original optical signal, and reducingthe intensity of optical noise of wavelengths longer than andwavelengths shorter than about the wavelength of the original opticalsignal.
 20. The method of claim 18 wherein the step of filtering opticalnoise comprises at least one step of reducing the intensity of opticalnoise of wavelengths longer than about the wavelength of the reflectedoptical signal, reducing the intensity of optical noise of wavelengthsshorter than about the wavelength of the reflected optical signal, andreducing the intensity of optical noise of wavelengths longer than andwavelengths shorter than about the wavelength of the reflected opticalsignal.
 21. The method of claim 18 further comprising the step ofincreasing the transmission of the original optical signal through thepad using an antireflection coating applied to the pad.
 22. The methodof claim 18 wherein the step of optical filtering involves using only aportion of the pad.
 23. The method of claim 18 wherein the step ofoptical filtering substantially prevents transmission of optical noisehaving wavelengths shorter than about 450 nanometers and optical noisehaving wavelengths longer than about 700 nanometers.
 24. A pad foroptically monitoring and processing the surface of a substrate, the padhaving a polishing surface; at least a portion of the pad comprising awindow material; the window material being capable of transmitting anoptical signal for optically monitoring the substrate; the window beingcapable of filtering predetermined optical wavelengths so as toattenuate optical noise; the window material having a surface recessedrelative to the polishing surface of the pad.
 25. The pad of claim 24wherein the window material is recessed a distance of about 300micrometers.
 26. The pad of claim 24 wherein the window material isrecessed a distance from about 5% to about 75% of the thickness of thepad.
 27. The pad of claim 24 wherein the window material is recessed adistance from about 5% to about 50% of the thickness of the pad.
 28. Apad for optically monitoring and processing substrates, the pad having apolishing surface; at least a portion of the pad comprising a windowmaterial; the window material being capable of transmitting an opticalsignal for optically monitoring the substrate; the window materialhaving reflection losses of less than 4% for a wavelength of the opticalsignal.
 29. The pad of claim 28 wherein the window material comprises anantireflection coating.
 30. The pad of claim 28 wherein the windowmaterial comprises a surface having a texture for reduced opticalreflection.
 31. The pad of claim 28 wherein the window material hasreflection losses of less than about 3.5%.
 32. The pad of claim 28wherein window material has reflection losses of less than about 3%. 33.A pad for optically monitoring CMP processes, the pad having a polishingsurface; at least a portion of the pad comprising a window material; thewindow material being capable of transmitting an optical signal foroptically monitoring CMP processes; the window material comprising aresin and at least one of
 1. a matrix of microfibers and
 2. amultiplicity of microspheres for increasing the strength of the windowmaterial.
 34. A pad for optically monitoring and processing substrates,the pad having a polishing surface; at least a portion of the padcomprising a window material; the window material being recessed fromthe polishing surface; the window material being capable of transmittingan optical signal for optically monitoring the substrate; the windowmaterial comprising a dye; the dye having optical properties so that thepresence of the dye allows transmission of a band of optical wavelengthsthat substantially include the optical signal while attenuatingtransmission of optical noise; the window material having reflectionlosses of less than about 4% for a wavelength of the optical signal; thewindow material comprising a resin; the window material comprisinghardeners; and the window material comprising microfibers for increasedstrength.